Reaction, chain, copolymer molar mass

For analyzing structure-property relationships, a variety of PEO-g-PVA copolymers were prepared, differing in the VAc-to-PEO ratio and the molar mass of PEO. The analysis of the copolymers by IR and 1H- and 13C-NMR showed the presence of both PEO and PVA. A small C=0 absorption was still present and was explained by a nonquantitative saponification. SEC showed polydispersities (Mw/M ) of around 5, with a small tailing to the low molar mass side. The latter was probably caused by the relatively low molar mass PVA homopolymer formed by the chain transfer reaction of VAc, both to the PEO and its acetate functionality. 

Figure 4 shows typical SEC profiles of two PS-3-PI diblock copolymers before and after the photodimerization reaction. [46] The appearance of a peak after the UV irradiation at a short retention time with a doubled molar mass indicates the formation of PS-3-PI-C-PI-3-PS copolymer chains. In contrast, the irradiation of SI 42 in THF without the self-assembly only leads to a slight increase of the molar mass. It confirms that the self-assembly helps to concentrate and expose the reactive ends of precursor diblock copolymers on the periphery of the core-shell micelles, which greatly increases the coupling efficiency of the photodimmerization reaction between two coumarin end groups. 

Rubbers and PESs are initially miscible with cyanate ester monomers. Phase separation occurs during the reaction. By plotting the phase diagrams (temperature vs. conversion), it is possible to compare the effects of chain ends and AN content in butadiene-acrylonitrile random copolymers and the effect of molar mass in PES. The cyanate ester monomer based on bisphenol A is a better solvent than DPEDC, and both dicyanates are better solvents than DGEBA. 

Synthetic polymers are produced by chain polymerization or step growth polymerization. Due to differences in the lifetime of activated species or the size and reactivity of the oligomers which are coupled in each reaction step, synthetic polymers are heterogeneous in molar mass. Copolymers are produced from more than one monomer species. In general, the different monomer species are differently incorporated in the polymer chain which causes distribution in chemical composition. Distributions in molar mass and chemical composition are also to be expected in polymers derived from homopolymers by incomplete chemical modifications, e.g. in partially hydrolyzed poly(vinyl acetate) [1]. 

A recently discovered quantitative radical chain-couphng reaction of polymer precursors preformed by CMRP, which is referred to as cobalt-mediated radical couphng (CMRC), was first observed when PAN-Co(acac)2 chains were treated with a large excess of isoprene at room temperature [58]. Instead of the formation of an expected PAN-h-polyisoprene (PI) diblock copolymer, a weU-defined homo PAN sample, with an exactly twofold higher molar mass compared to the precursor, was recovered. Interestingly, this coupling reaction proved to be quantitative. 

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